This invention relates generally to application of maskants to metal surfaces to be subjected to chemical etching or milling; more specifically, it concerns the solving of problems that have arisen in this field.
At present, it is usual practice to dip the article or part to be coated at least twice in the maskant bath in order to obtain the desired uniform thickness. Thus for example, the part will be suspended or supported and dipped once (down and up) into the bath to produce a tapered coat; and the part will then be vertically reversed, and dipped again to produce a reversely tapered coat. The two coats then add up to a generally uniform lateral thickness along the vertical length of the surface. Such practice not only requires two dips, which are time consuming and hence costly, but other problems ensue. For example, it is common experience that drainage of the maskant liquid off the part and back into the bath results in air entrainment. Pin hole air bubbles are formed in the bath due to such air entraining drainage, and the bubbles then become located in films formed on subsequently dipped parts, which produce defects upon chemical etching or milling.